1. Field of the Invention
The invention pertains to isolation of protein and starch constituents from wheat flour. More particularly, a methodology of isolation enhances the properties and protein content of isolated protein constituents.
2. Description of the Related Art
Wheat gluten is the natural water-insoluble protein portion of wheat endosperm which, during wet processing of wheat flour, is separated in the form of a protein-lipid-starch complex. Commercial wheat gluten has a mean composition of 72.5% protein (77.5% on dry basis), 5.7% total fat, 6.4% moisture and 0.7% ash; carbohydrates, mainly starches, are the other major component. The major protein fractions of wheat gluten consist of gliadin and glutenin which differ in their solubility properties and molecular weight.
Wheat gliadins consist of about 50 different single-chained proteins with molecular weights of 30,000-100,000 daltons. When isolated, gliadins are very sticky, which apparently is responsible for the cohesion property of wheat gluten. By contrast, glutenin proteins are multi-chained, polymerized by disulfide bonds, and larger in size with molecular weight of about 3,000,000 daltons. Upon isolation, glutenins exhibit resiliency but neither cohesion nor extensibility and, therefore, appear to give wheat gluten its elastic properties.
Wheat gluten is unique among cereal and other plant proteins because of its capacity to form a cohesive and viscoelastic mass suitable for breadmaking. The viscoelasticity appears to be because the gluten proteins are water compatible and, thus, will swell and interact. As water is taken up by wheat gluten, it goes through a glass transition where it changes from a hard glassy material to one that is rubbery and elastic. Wheat gluten is also unique in its ability to impart to wheat flour doughs the property to retain leavening gases. Other unique properties of wheat gluten are: appropriate balance in the content of gliadin and glutenin, unusually high content of the amino acid glutamine, and extreme polydispersity of its molecular weight. These unique properties define gluten's superior performance in a variety of products.
The uses of wheat gluten are wide-ranging and, during the last decade, its utilization has intensified. Although the uses of wheat gluten can vary from country to country, baking represents the predominant usage of wheat gluten, accounting for 63% of total usage worldwide. In the European Union, flour fortification ranks a close second to baking usage with pet food applications ranking third. The second leading use of wheat gluten worldwide and in North America and Australia is in pet foods. Baking, imitation meats/fish, and processed foods are the major uses of wheat gluten in Japan. In Japan, wheat gluten is also used for the preparation of bread known as “Fu” bread, for the production of monosodium glutamate as a seasoning agent, and for the preparation of gluten hydrolyzate for use as an extender for soy sauce called “Sho-yu”. Wheat gluten also plays an important role in the creation of vegetarian food for the 309 million Buddhists worldwide and the 100 million Chinese Buddhists in which Chinese-style meat analogs have been made from wheat gluten by hand or simple extrusion.
As reported by Maningat and Bassi, Wheat Starch Production, Program Proceedings of the International Starch Technology Conference, pp. 26-40 (University of Illinois, 1999), which is incorporated by reference to the same extent as though fully disclosed herein, there are several processes for industrial production of wheat gluten, and they typically are named after the company or the person who developed or patented the process. These processes include: Martin, Batter, Hydrocyclone, Pillsbury Hydromilling, Modified “Fesca”, Alkali, Far-Mar-Co. and Tricanter (also variously referred to as Wesffalia Centrifuge HD, Flottweg Tricanter, Barr & Murphy, or Decanter-Based Weipro).
Differences exist among these processes in terms of type of raw material (whole wheat vs. flour, hard wheat vs. soft wheat, etc.), dispersion procedure (water vs. chemical), consistency of wheat flour/water mixture (dough vs. batter), and equipment for starch and gluten separation (centrifuge vs. shaker screen vs. hydrocyclone vs. agitator/ribbon blender).
The Martin, Batter, Hydrocyclone, Raisio/Alfa-Laval and Tricanter processes are regarded as among the most popular manufacturing methods for wheat gluten production. The choice of a process to produce wheat gluten is dependent on a number of different factors. In order to produce wheat gluten, it is necessary to have three things: (a) a good source of raw material flour, (b) a way to process wheat starch that is a co-product in a ratio of up to 6 (starch) to 1 (gluten), and (c) a method of handling the effluent water from the gluten and starch manufacturing process. In cases where sub-quality flour is used, the use of the enzymes pentosanases and cellulases is recommended to improve gluten yield and starch recovery. Other important factors involved in the production of wheat gluten are the yield of wheat gluten, water balance, pH of flour slurry, the cost of a system from a capital standpoint, and the operating costs of the system.
Water consumption is a historical problem in the art. The Martin and Batter processes have historically used as much as 15 pounds of fresh water for every pound of flour that is processed, i.e., a ratio of 15:1. Disposing of this water volume in an ecologically effective way is difficult. Recycling of process water may reduce the ratio down to 6:1. Ratios for other processes include Hydrocyclone (4.5:1), Decanter (4:1), and High Pressure Disintegration (from 2:1 to 3:1).
Historically, the Martin process, developed in Paris in 1835, was among the earliest and most successful process for the recovery of wheat gluten. A flow diagram of the generalized Martin process is shown in FIG. 1 (discussed in detail below), but variations of this process are widely practiced. The Martin process utilized wheat flour as the starting raw material and water was added in a mixer to form a dough. The dough was allowed to develop so that it was thoroughly hydrated. It then would undergo an extraction step where more water was added to begin the separation process between the gluten and the starch. The dough washing step is designed to release the starch without dispersing or breaking up the gluten into small pieces. Sufficient water is used to wash the starch from the dough while it is kneaded or rolled; devices such as ribbon blenders, rotating drums, twin screw troughs, and agitator vessels have been designed for this purpose. The wet gluten would then be mechanically separated from the starch in rotating or vibratory screens to achieve a gluten with a protein content of 75% (dry basis). The major drawback to this system was the excessive use of water, as much as 10 to 1, which complicates starch recovery and presents a significant effluent problem which has to be addressed. Modifications of the process have been utilized in the industry for years.
The Batter process was invented in 1944. In this process, the batter is prepared by mixing flour and water to yield suspended curds of gluten from which the starch has been washed out. The curds are recovered on a gyrating screen and the starch milk passes through. The starch is refined through a series of screens, sieves and centrifuges, and dried as in the Martin process.
In the Hydrocyclone process, a batter formed with recycled wash water and flour is introduced directly into a series of hydrocyclones. The “A” starch is washed out directly with counter-current fresh water. Because of the intense fluid shear in the hydrocyclones, the gluten agglomerates into small curds rather than large lumps. The gluten curds can be washed and separated on a rotating washer screen. The main advantage of this process is its low usage of water. Older plants, based on the Martin or the Batter process, are being retrofitted with hydrocyclones to lower operating costs and almost eliminate effluent waste.
FIGS. 1-4 relate to various commercial processes that are used to separate wheat gluten form starch. It will be appreciated that the processes and process equipment have various commercial embodiments that may differ slightly as implemented in different commercial plants. The process goals are to provide wet processing of wheat flour in a manner that facilitates physical separation of gluten from starch materials on a density or sieve basis.
FIG. 1 is a block schematic diagram showing flow stream linkage of commercially available components combined in a manner that implements, generally, the Martin process 100. Process input feeds include milled wheat flour 102 and water 104, which a dough mixer 106, such as a pin mixer, combines in a ratio of 10 parts flour to 8 parts water by weight. A typical temperature for water 104 submitted to mixer 106 is 90.degree. F. Mixer 106 discharges into a residence or maturation tank 108 where the dough rests while hydrating to completeness. With discharge from the maturation tank 108, an additional volume of water 110, for example, five parts by weight per unit of wheat flour 102, is introduced to the flow stream, and the combination is vigorously mixed in an agglomerator 112, which is for example a turbulator. The action of agglomerator 112 works on the flow stream to provide gluten as elastic curds bathed in a milky starch suspension. Agglomerator 112 discharges into a separating screen 114, such as a reel—an elongated and slanted hollow rotating cylinder typically equipped with 40 mesh screen. The portion of the flow stream that is the milky starch suspension passes through the separating screen 114, as isolated A starch 116 subject to downstream purification processes 118. The downstream processes may include conventional sieving to remove successively smaller gluten particles 120, centrifugation and/or hydrocyclone processing to concentrate the starch 122.
Separating screen 114 retains the gluten as a doughy mass. Optional water jets 124 positioned on the separating screen 114 may facilitate washing and discharge of the gluten from separating screen 114. Separating screen 114 discharges into a kneader 126, such as a conventional mixer. The action of kneader 126 releases starch from the gluten matrix. The starch is suspended in water, as so it is appropriate to dewater the gluten by suitable agents, such as a dewatering screen 128, which may be a second reel, followed by a dewatering press 130. By way of example, the dewatering press 130 may be a screw press.
The dewatered gluten flow stream may be submitted to a flash dryer 132 to yield wheat gluten 134. Alternatively, output from the dewatering press 130 may be processed without drying in flash dryer 132 to form wheat protein isolate, hydrolyzed wheat protein, deamidated wheat gluten, or other modified wheat gluten.
It will be appreciated that filtrate from the dewatering screen 128 may be submitted to B starch processes 136 for the isolation of B starch. Purified B starch is somewhat inferior to A starch and may in some instances be used for animal feed or as a feedstock for chemically modified starches.
FIG. 2 is a block schematic diagram showing flow stream linkage of commercially available components combined in a manner that implements, generally, the Hydrocyclone process 200. This is the dominant commercial process at the present time. Equipment advantages include compactness, less expense to install, lower water usage, and fewer moving parts. In FIG. 2, as in the drawings that follow, like numbering is retained with respect to identical conceptual system components shared with the Martin process equipment of FIG. 1 and other figures.
Residence time of dough in the maturation tank 108 persists for about 10 to 20 minutes. Maturation tank 108 discharges into a dispersion tank 202 The action of dispersion tank 202 differs from that of agglomerator 112 (shown in FIG. 1) because dispersion tank 202 uses less turbulence to mix the dough from maturation tank 202 with water 110 and form a uniform suspension, as opposed to the formation of gluten curds in agglomerator 112. Dispersion tank 202 discharges into a multistage hydrocyclone system 204 that may be equipped with a rotary strainer to remove larger agglomerates which can plug the cyclones. By way of example, the hydrocyclone system 204 may be a fifteen-stage hydrocyclone.
Wheat gluten has a density of 1.1 g/cc, whereas starch has a density of 1.4 g/cc. The hydrocyclone system 204 operates on this density difference to separate the gluten from the starch suspension 206. Gluten is collected as overflow and starch is collected as underflow. The starch suspension 206 may be purified by downstream processes 208, such as sieving, further hydrocyclone processing to concentrate the starch suspension 206, and drying to yield wheat starch.
Spontaneous agglomeration of gluten occurs in the hydrocyclone system 204 due to the shear forces that inherently affect the flow stream in hydrocyclone system 204. Hydrocyclone system 204 discharges into a washing screen 210. The washing screen 210 may be an inclined static screen, which is used to separate the gluten from B starch, bran, and cell wall materials. Further refinement of gluten proceeds through dewatering screen 128, dewatering press 130, and flash dryer 132 as discussed in context of FIG. 1.
FIG. 3 is a block schematic diagram showing flow stream linkage of commercially available components combined in a manner that implements, generally, the Alfa-Laval/Raisio process 300. Flour 102 and water 104 are mixed in ratios that form a thick batter, which is thinner than a dough. A batter mixer 302, such as a pin mixer, which discharges into a disc disintegrator 304. The disc disintegrator operates on the batter to form a substantially homogenous suspension of starch, protein and other components. A decanter centrifuge 306 separates the protein or gluten fraction 308 from the starch fraction 310. The gluten fraction 308 typically has about 40% protein and the starch fraction 310 about 1% protein at this point. The gluten fraction is discharged into a maturation tank 312, which is equipped with a slow speed agitator that builds clots or threads of gluten. A disc disintegrator 314 completes the gluten agglomeration by forming lumps that can be separated from the flow stream and discharges into a vibrating screen 316. The vibrating screen 316 separates the gluten from bran and starch 318. A dewatering press 130, such as a screw press, removes water from the gluten, which may then be optionally flash dried in a flash drier 132 to yield wheat gluten.
The prime starch fraction 310 is processed by rotating conical screens 324 to remove fibers. A first decanter 326 washes the flow stream in countercurrent mode, and a second decanter 328 concentrates the starch, which usually has a protein concentration of about 0.3% when submitted to drier 330.
B starch 318 is rich in starch and solubles, which are recovered using a decanter 332. A nozzle or solids-ejecting centrifuge 334 concentrates the B starch to about 25% solids. A dewatering device 336, such as a decanter centrifuge, further dewaters the B starch 318 prior to discharge into a drier 338. Solubles 340 discharged from centrifuge 334 may be dried using a drier 342.
FIG. 4 is a block schematic diagram showing flow stream linkage of commercially available components combined in a manner that implements, generally, Tricanter process 400, which is alternatively known in the art as the Wesffalia Centrifuge HD process, Flottweg Tricanter process, Barr & Murphy process, or Decanter-Based Weipro process. Mixer 106 combines flour 102 and water 104 in ratios that form a dough. The dough is pumped into a high intensity homogenizer 402 that imposes sufficient shear forces on the dough to disintegrate the gluten-starch matrix, forming an emulsion. A three-phase decanter 404 separates this emulsion into an A starch stream 406, a gluten plus B starch stream 408, and a pentosans and solubles stream 410. The three-phase decanter may be, for example, a horizontal, conical bowl centrifuge equipped with a screw conveyor, as is known in the art.
The A starch stream 406 typically contains less than 1% protein. An eight stage hydrocyclone 412, washes and concentrates the A starch stream 406. Fiber removal is accomplished using a combination of rotary and static screens 414, followed by further concentration using a three stage hydrocyclone 416. A dewatering device 418 provides further concentration, followed by submission to a drier 420. The gluten and B starch stream 408 is processed through a rotary screen 422 to remove the gluten, which is transferred to a rotary washer 424. A dewatering screw press 130 removes water from the recovered gluten, which is then submitted to flash drier 132.
Filtrate from the rotary screen 422 contains A starch and B starch. The filtrate travels to a disc bowl separator 430, which separates the A starch from the B starch. The A starch is submitted to the eight stage hydrocyclone 412 to obtain a nearly complete A starch recovery. The rotary cone screens 432 sift the bran/starch stream to remove fiber 434. A nozzle separator 436 preconcentrates the B starch, which is followed by further dewatering in decanter 438 to provide concentrated B starch 440.
The early separation of pentosan and solubles stream 410 beneficially concentrates the A starch stream 406 and the gluten and B starch stream 408, while also reducing the viscosity of these other streams. Total effluent wastes from process 400 are, consequently, reduced. Fine gluten remaining in the pentosan and solubles stream 410 is removed by gluten screen 442 and provided to the rotary gluten washer 424. Filtrate from gluten screen 442 travels to rotary cone screens 444 for clarification and subjected to drying in an evaporator 446.
The process equipment schematics of FIGS. 1-4 produce, generally, a wheat gluten 134 having a protein content of 75% minimum (dry basis). As previously indicated, wheat gluten that contains 77.5% protein (dry basis), 5.7% total fat, 6.4% moisture, and 0.7% ash, has contaminants of 9.7% by weight. These contaminants may include, typically, B starch, bran and/or fibers. Contaminants of this magnitude may affect organoleptic qualities of the wheat gluten, particularly when the wheat gluten is processed to make vegetarian snacks and/or treats. Shelf life may also be affected when the contaminants include starch, which tends to adsorb atmospheric water.